One of the many exciting technologies from the Saturn-V was the F-1 engine. That technology has not been exploited since the Saturn-V was discontinued which IMHO was a big mistake. One of my pet ideas is to develop an RLV based upon a TSTO biamese architecture with easily removable and interchangable cores. The airframe would essentially be a suit of clothing with a structurally robust thermal protectection system. The cores would establish the specific stages function, i.e. either a booster or an orbit vehicle. The booster would use a couple F-1 engines with kerosene fuel. The orbit vehicle would use a couple SSME or J-2 with hydrogen fuel. The system would be designed such that a core could be inserted one or two days before launch. If a specific airframe or core got flakey, then the whole stack could be disassembled with the flakey part replaced inside a couple of days. The key concept is interchangability based upon a single air frame design using established technology.

Gary